1. Field of the Invention
This invention relates to agricultural machines and, more particularly, to means for detecting foreign objects, such as stones, collected along with the crop material being harvested.
2. Description of the Prior Art
Harvesting machines such as combine harvesters (hereinafter referred to as a combine) are susceptible to damage by foreign objects such as stones and other hard objects (hereinafter referred to simply as "stones") ingested therein during the harvesting process. Stone detecting and eliminating systems for protecting the combine are known in the prior art. For example, U.S. Pat. Nos. 3,675,660 and 3,805,798 entitled "Combine Stone Trap Door" and "Combine Harvester Protection System", respectively, both in the name of C. F. Girodat and both assigned to Massey, Ferguson Industries, disclose detector systems for eliminating rocks from a combine in which a piezoelectric element, attached to the bottom of the combine's header table assembly, generates output signals in response to acoustical vibrations induced therein. The electrical signals, moreover, are filtered and if of sufficient amplitude, indicative of a stone are applied to a trap door, a declutching mechanism or a combination thereof for eventual elimination of the object.
The known detection and elimination systems are subject to serious disadvantages, however. For example, directly coupling the piezoelectric element or stone detector system to the bottom of the combine's header table assembly subjects the system to spuriously induced vibrations or signals such as those due to the interaction of the moving mechanical members of the combine, to "stones" outside the combine which make contact therewith and due to the impact of the table assembly with the ground. These interactions involve relatively hard materials resulting in characteristic acoustical vibrations induced in the sensor similar to those vibrations created by the "stone"-sensor surface contact which the system is attempting to detect. Accordingly, the spurious or false signals or those acoustic vibrations of the same character as the "stone"-sensor surface contact will result in an increased false alarm rate resulting in, for example, unnecessarily activating the trap door mechanism. As spurious signals or an increased false alarm rate results in lost time and crop material, sensitivity of the system may be reduced to decrease the effect of the spurious signals. However, a reduced sensitivity increases the chances that some stones will not be detected resulting in machine damage.
The detector and eliminator systems of the prior art have several further limitations with respect to the sensor system and elimination means and lost crop material. Typically, each combine uses at least two headers, such as a direct-cut header and a corn header, for different crops. Additionally, the direct-cut headers may be adapted for particular crops by using a pick-up header attachment, a soybean pick-up reel, or a grain bat reel. If the piezoelectric element of the detector system is disposed within the table assembly of the header, a sensing device must be incorporated in each header of a single combine. For example, the table assembly of the header is typically 12 to 20 feet in width whereas the feeder housing or crop elevator which is fed by an auger in the header is generally about 40 inches in width. Accordingly, the flow of material in the table assembly is much slower than in the crop elevator. Moreover, as the eliminating system, conventionally a trap door, is generally disposed within the crop elevator, there is a substantial difference in the time of detection and elimination of the stone from one portion of the header as compared to the time of detection and elimination from another portion. Thus, in order to insure the elimination of the stones from the harvested crop, the trap door must remain open for a relatively long period of time permitting substantial amounts of crop to be lost.
In addition, it is apparent that unless virtually all of the "stones" gathered by the combine are insured of contacting the detector system, regardless of the size thereof, or the amount of crop material being harvested, a substantial number of non-contacting and, therefore, non-detected stones will be transported with the crop material into the threshing components of the combine where substantial damage may result.
Accordingly, there is a need for a "stone" detector system which will overcome or at least alleviate the problems associated with the prior art systems as described hereinabove and which insures the detection of virtually all of the stones entering the combine.